Now the MacMillan family are lobbying the Federal Government to raise awareness to prevent further deaths.

"I just want my boy back. I still am finding it very hard to accept that this has happened," his mother Michelle told PM.

"I just have terrible days sometimes, can't stop crying," said Jack's father George.

"I still can't believe that my boy is gone, and like Michelle I just want him back and he's not coming back. I miss him."

I just have terrible days sometimes, can't stop crying. I still can't believe that my boy is gone, and like Michelle I just want him back and he's not coming back. I miss him.

George MacMillan

Ms MacMillan says her son was doing what countless other children do; underwater laps, challenging himself to hold his breath for long periods.

"He just thought it was great. It was something he had been doing over the Christmas holidays with friends and family in the pool," she said.

"I'd been watching and I had my baby and momentarily took my eyes off the pool.

"I looked back and I saw him at the bottom of the shallow end of the pool and his knees were bent up almost as if he was in the foetal position and I thought, is he playing?"

Neither Jack nor his mother had any idea that what he was doing could be so dangerous.

"Such a silly simple thing that so many kids do," she said.

"So many parents, I think every parent I've spoken to since Jack died. Nobody knew. Nobody has heard of shallow water blackout."

Swimmers increase their levels of carbon dioxide and decrease oxygen when they hold their breath.

If they lose consciousness and breathe in, their lungs can fill with water.

John Lipman from the Diver Alert Network says repetitive breath holding is a common practice among free divers that requires close supervision.

"Unless they're grabbed immediately by somebody supervising them and pulled out of the water before they breathe they're at risk of drowning," he said.

Calling for change

Justin Scarr from Royal Life Saving Australia (RLSA) says while there have only been five cases of shallow water blackout in the past 10 years, he suspects many go unreported.

"We do believe that there are several other cases that may in fact not appear on our drowning database," he said.

"If the drowning is unwitnessed, the coroner may be reluctant to make a specific finding that cites shallow water blackout."

We do believe that there are several other cases that may in fact not appear on our drowning database. If the drowning is unwitnessed, the coroner may be reluctant to make a specific finding that cites shallow-water blackout.

Justin Scarr, Royal Life Saving Australia

Sharon Washbourne, Jack MacMillan's aunt, says she is determined to raise awareness of the dangers of shallow water blackout.

"If I know that I can save one life let alone 1,000 it would help in Jack's legacy to keep the awareness going and it helps us remember him," she said.

The MacMillan family want increased education and mandatory warning signage in all pools, a move supported by RLSA.

"If we find that shallow water blackout is an ongoing issue, an underreported issue, I believe there is a case in terms of making compulsory signage on this particular issue," Mr Scarr said.

Federal Sports Minister Kate Lundy says she is working with RLSA to build warnings into existing water safety campaigns.

"I believe there is a serious opportunity here to build messages about the dangers of holding your breath for extended periods underwater and how that can lead to shallow water blackout and tragic deaths," she said.

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